10. Error Handling, Debugging and Testing.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
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   "source": [
    "# Error Handling, Debugging and Testing"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Sections\n",
    "- [Error handling](#Error-handling)\n",
    "- [Debugging](#Debugging)\n",
    "- [Testing](#Testing)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Error handling\n",
    "\n",
    "Syntax errors are identified at compile time, before running the script. It happens when the programmer did not follow Python syntax.\n",
    "Exception errors are run-time errors. It does not stop the excecution of the entire script."
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Usually errors give a hint about what happened. Typical errors are:\n",
    "- NameError\n",
    "- TypeError\n",
    "- SyntaxError\n",
    "- IndexError\n",
    "- KeyError:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 1,
   "metadata": {},
   "outputs": [
    {
     "ename": "SyntaxError",
     "evalue": "invalid syntax (<ipython-input-1-8771c72daece>, line 1)",
     "output_type": "error",
     "traceback": [
      "\u001b[1;36m  File \u001b[1;32m\"<ipython-input-1-8771c72daece>\"\u001b[1;36m, line \u001b[1;32m1\u001b[0m\n\u001b[1;33m    for x in range(3)\u001b[0m\n\u001b[1;37m                     ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m invalid syntax\n"
     ]
    }
   ],
   "source": [
    "# This is a syntax error, because we did not folow the Python rules. an DILE can identify this errors.\n",
    "for x in range(3)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "ename": "NameError",
     "evalue": "name 'my_var' is not defined",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-3-56587a39d030>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mmy_var\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mNameError\u001b[0m: name 'my_var' is not defined"
     ]
    }
   ],
   "source": [
    "my_var"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 36,
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "unsupported operand type(s) for +: 'int' and 'str'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-36-ca9a4a080236>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[1;31m# for example with this error\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 2\u001b[1;33m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m1\u001b[0m\u001b[1;33m+\u001b[0m\u001b[1;34m\"a\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m: unsupported operand type(s) for +: 'int' and 'str'"
     ]
    }
   ],
   "source": [
    "# for example with this error\n",
    "print(1+\"a\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Try and except keyworks\n",
    "\n",
    "When an error happens, ussually the script stops it execution.\n",
    "If we want to avoid that, we can use try and except blocks"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 37,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "something went wrong\n"
     ]
    }
   ],
   "source": [
    "# the try and except keywords, avoid a program to crash or exit \n",
    "try:\n",
    "    print(1+\"a\")\n",
    "except:\n",
    "    print(\"something went wrong\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 40,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "What is your age? keti\n"
     ]
    },
    {
     "ename": "ValueError",
     "evalue": "invalid literal for int() with base 10: 'keti'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mValueError\u001b[0m                                Traceback (most recent call last)",
      "\u001b[1;32m<ipython-input-40-1ccd6323f589>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mage\u001b[0m \u001b[1;33m=\u001b[0m \u001b[0mint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0minput\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"What is your age? \"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m\u001b[0;32m      2\u001b[0m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[0mage\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n",
      "\u001b[1;31mValueError\u001b[0m: invalid literal for int() with base 10: 'keti'"
     ]
    }
   ],
   "source": [
    "# A very typical error in object conversiom\n",
    "age = int(input(\"What is your age? \"))\n",
    "print(age)"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Try, except and else keyworks\n",
    "\n",
    "The else block is executed only if the except block is not executed."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 43,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "What is your age? keti\n",
      "Please enter a number\n",
      "What is your age? 0\n",
      "0 is not a valid age, please enter a number greater than 0\n",
      "What is your age? 1\n",
      "1\n",
      "Thank you\n"
     ]
    }
   ],
   "source": [
    "# Now with try and except\n",
    "while True:\n",
    "    try:\n",
    "        age = int(input(\"What is your age? \"))\n",
    "        1/age                            # validates is not a zero\n",
    "        print(age)\n",
    "    except ValueError:\n",
    "        print(\"Please enter a number\")\n",
    "    except ZeroDivisionError:\n",
    "        print(\"0 is not a valid age, please enter a number greater than 0\")\n",
    "    except:\n",
    "        print(\"The value entered not valid\")        \n",
    "    else:                                 # else is executed is except is not executed\n",
    "        print(\"Thank you\")\n",
    "        break"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 56,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "Please, enter numbers! \n",
      "Error message: \n",
      "unsupported operand type(s) for /: 'int' and 'str'\n",
      "\n",
      "Please, enter numbers! \n",
      "Error message: \n",
      "division by zero\n"
     ]
    }
   ],
   "source": [
    "# Another example\n",
    "def sum(num1, num2):\n",
    "    try:\n",
    "        num1/num2\n",
    "        return num1 + num2\n",
    "    except (TypeError, ZeroDivisionError) as err:\n",
    "        return f\"Please, enter numbers! \\nError message: \\n{err}\"\n",
    "    \n",
    "print(sum(1,\"a\"))\n",
    "print(\"\")\n",
    "print(sum(1,0))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Try, except, else and finally keyworks\n",
    "\n",
    "The finally block is always executed with or without error.\n",
    "\n",
    "Is used commonly to liberate resourecs like closing file, clossing connections, etc."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 3,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "What is your age? hola\n",
      "Please enter a number\n",
      "ok, finally we are done!\n",
      "What is your age? 0\n",
      "0 is not a valid age, please enter a number greater than 0\n",
      "ok, finally we are done!\n",
      "What is your age? 3\n",
      "Thank you\n",
      "ok, finally we are done!\n"
     ]
    }
   ],
   "source": [
    "while True:\n",
    "    try:\n",
    "        age = int(input(\"What is your age? \"))\n",
    "        1/age                            # validates is not a zero\n",
    "    except ValueError:\n",
    "        print(\"Please enter a number\")\n",
    "    except ZeroDivisionError:\n",
    "        print(\"0 is not a valid age, please enter a number greater than 0\")\n",
    "    except Exception:                    # This optION IS FOR ANY OTHER EXCEPTION\n",
    "        print(\"The value entered not valid\")\n",
    "    else:                                 # else is executed is except is not executed\n",
    "        print(\"Thank you\")\n",
    "        break\n",
    "    finally:                              # Finally runs at the end after everything has run\n",
    "        print(\"ok, finally we are done!\")"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "### Raising errors"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Debugging"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Linting is a useful funtion to improve your code. It identifies errors even before running the code. it is integrated in several IDEs. Some useful utilities are:\n",
    "- pylint\n",
    "- pyflakes\n",
    "\n",
    "Stype checking utilities are also common to use.\n",
    "- PEP 8 utilities\n",
    "\n",
    "using print is very useful for checking and troubleshooting the code.\n",
    "Reading and intepretinge rros are very useful. Some are very common.\n",
    "\n",
    "### PDB\n",
    "\n",
    "Specifically for debugging, we have pdb funtion. This is a Python debugger that we have to import in order to use it. It has several tools, for example:\n",
    "- list\n",
    "- a\n",
    "- step\n",
    "- continue\n",
    "- clear\n",
    "- help\n",
    "\n",
    "We can use help inside to read the explanation of each tool, for example:\n",
    "- help list"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 5,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "> <ipython-input-5-2f6cdea0f110>(5)add()\n",
      "-> return num1 + num2\n",
      "(Pdb) a\n",
      "num1 = 2\n",
      "num2 = 3\n",
      "(Pdb) step\n",
      "--Return--\n",
      "> <ipython-input-5-2f6cdea0f110>(5)add()->5\n",
      "-> return num1 + num2\n",
      "(Pdb) continue\n",
      "5\n"
     ]
    }
   ],
   "source": [
    "import pdb\n",
    "\n",
    "def add(num1, num2):\n",
    "    pdb.set_trace()                    # A soon as it find set_trace, stops de execution of the code\n",
    "    return num1 + num2\n",
    "\n",
    "print(add(2,3))"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 8,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "> <ipython-input-5-2f6cdea0f110>(5)add()\n",
      "-> return num1 + num2\n",
      "(Pdb) a\n",
      "num1 = 2\n",
      "num2 = 3\n",
      "(Pdb) num1 = 5\n",
      "(Pdb) continue\n",
      "8\n"
     ]
    }
   ],
   "source": [
    "\"\" We can even change the values of the data (variables)\n",
    "print(add(2,3))"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "## Testing"
   ]
  },
  {
   "cell_type": "markdown",
   "metadata": {},
   "source": [
    "Testing is a proactive procedure to verify that the code works, ussually before the program is send to the public or customer.\n",
    "\n",
    "Usually you write an additional file (test.py) that you write to test your code."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Example of main.py\n",
    "def do_stuff(num):\n",
    "  try:\n",
    "    if num: \n",
    "      return int(num) + 5\n",
    "    else:\n",
    "      return 'Please enter a number.'\n",
    "  \n",
    "  except ValueError as err:\n",
    "    return err"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "metadata": {},
   "outputs": [],
   "source": [
    "# Example of test.py\n",
    "import unittest\n",
    "import main\n",
    "\n",
    "class TestMain(unittest.TestCase):\n",
    "    def test_do_stuff_1(self):\n",
    "        test_param = 10\n",
    "        result = main.do_stuff(test_param)\n",
    "        self.assertEqual(result, 15)\n",
    "\n",
    "    def test_do_stuff_2(self):\n",
    "        test_param = \"fdgd\"\n",
    "        result = main.do_stuff(test_param)\n",
    "        self.assertIsInstance(result, ValueError)\n",
    "    \n",
    "    def test_do_stuuf_3(self):\n",
    "        test_param = None\n",
    "        result = main.do_stuff(test_param)\n",
    "        self.assertEqual(result, \"Please enter a number.\")        \n",
    "        \n",
    "    def test_do_stuuf_4(self):\n",
    "        test_param = \"\"\n",
    "        result = main.do_stuff(test_param)\n",
    "        self.assertEqual(result, \"Please enter a number.\")        \n",
    "\n",
    "if __name__ == \"__main__\":\n",
    "    unittest.main()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": null,
   "metadata": {},
   "outputs": [],
   "source": []
  }
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